Fabric filter with gas inlet geometry and method

ABSTRACT

The present invention provides a fabric filter apparatus and a method of feeding dusty gas to the dusty gas section of a fabric filter apparatus. The housing (11) of the fabric filter apparatus includes at least one substantially vertically extending duct (13) the lower end of which is in fluid communication with the dusty gas inlet (31). The duct diverts a portion of the dusty gas entering the fabric filter apparatus and delivers it to a corner of the housing (11) at a position intermediate the level of the porting plate (40) and the bottom of the circular filter bag array (50).

TECHNICAL FIELD

The present invention relates to a fabric filter for the removal ofparticulate matter from a gas stream and more particularly to such afabric filter having an improved gas inlet geometry.

BACKGROUND OF THE ART

Fabric filters are known in which a gas stream to be cleaned is directedthrough a group of elongate filter bags from their outside to theirinside. The bags are periodically cleaned, such as by periodicallyinjecting into them, against the gas stream, a gas pulse which serves tobriefly reverse the direction of gas flow through the filter bags and tothereby remove from the outside of the bags particulate matter that hadbeen retained on the filter bags. U.S. Pat. No. 4,157,899 discloses sucha fabric filter.

In fabric filters of this type the group of filter bags is typicallydisposed in a housing body having a dusty gas section with an inletthereto and a clean gas section with an outlet therefrom. A portingplate is mounted in the housing body separating the dusty and clean gassections and has a plurality of concentric rings of ports. A filter bagis supported from each port in the porting plate and hangs into thedusty gas section. A backflushing means are mounted in the clean gassection and are adapted to direct gas pulses to sequentially backflushthe filter bags.

In most known fabric filter dusty gas is discharged directly into thedusty gas section of the fabric filter housing. Although inexpensive,this method of entry creates a great deal of turbulence and unevenvelocities between filter bags which can result in bag abrasion andre-entrainment of dust following pulsing. It is also known to provide aplenum between the filter bags and a wall of the housing across itswidth. This allows the dusty gas to enter the housing at lowervelocities than would otherwise be the case. Such plenums are, however,wasteful of space and for this reason have not been universallyaccepted.

SUMMARY OF THE INVENTION

In a first broad aspect, the present invention provides a fabric filterapparatus having a housing defining a dusty gas section with an inletthereto and a clean gas section with an outlet therefrom, a portingplate mounted in the housing separating the dusty gas section from theclean gas section and a substantially circular array of fabric filterbags depending therefrom; said housing further including ageneration/distribution means to generate pulses of backflushing gas anddistribute them periodically into the open upper ends of the fabricfilter bags through respective ports in the porting plate, wherein atleast one duct is provided in the housing, the bottom of the duct beingin fluid communication with the inlet, the top of the duct opening intoa corner of the housing at a level intermediate the inlet and theporting plate.

The inlet of the inventive fabric filter apparatus may be elongated inthe horizontal direction with the duct being in fluid communication witha lateral end of the inlet. It is also possible to provide two suchducts in fluid communication with opposite lateral ends of the inlet.

Preferably, the housing is provided with a plurality of substantiallyplanar sides eg. four planar sides to form a square or rectangle, and isprovided with two substantially vertically extending ducts disposed inadjacent corners of the housing.

The inlet of the housing is preferably positioned to open into adownwardly tapering hopper forming the lower end of the housing. Adamper may be mounted in the inlet to control gas flow into the housing.

The lower portion of each duct is also preferably provided with a bleedaperture sized to allow particulate matter falling out of the dusty gasstream to escape from the duct.

In a second broad aspect, the present invention provides a method offeeding a dusty gas to a dusty gas section of a fabric filter, saidfilter further including a clean gas section, a porting plate mountedbetween the dusty gas section and clean gas section with a circulararray of fabric filter bags depending from the porting plate and ageneration/distribution means to generate pulses of backflushing gas anddistribute them periodically into the open upper ends of the fabricfilter bags through respective ports in the porting plate, said methodcomprising feeding a first portion of the dusty gas directly into thehousing at a position below or adjacent the bottom of the fabric filterbag array and diverting a second portion of the dusty gas from the inletand delivering the diverted dusty gas to at least one corner of thehousing at a level intermediate the inlet and the porting plate.

The second portion is preferably between 10% and 90% of the total dustygas flow entering the filter.

Preferably, the dusty gas is fed to the dusty gas section via an inletelongated along one side of the housing. The dusty gas is preferablydiverted substantially vertically from either or both lateral ends ofthe elongated inlet opening.

Most preferably the housing is provided with a plurality ofsubstantially planar sides with dusty gas being diverted vertically fromboth lateral ends of the inlet and delivered to adjacent corners of saidhousing at a level intermediate the inlet and the porting plate.

The arrangement according to the present invention has four substantialadvantages over the prior art. Firstly, by introducing gas further upthe filter bag array there is a significant reduction in the plan areaand in the capital construction cost. This is achieved by the gas in thevertically extending ducts travelling at velocities significantly higherthan can be tolerated by the filter bags and by utilising the previouslyunused corners of the housing which surround the circular array offilter bags. Secondly, flow patterns into the array of filter bags areimproved by introducing gas further up the bag array promoting asideways and downward gas flow from the ducts and thereby maximisingparticulate preseparation i.e. the entrained particulate matter droppingout of the gas stream and falling into the hopper without having beentrapped on the surface of a filter bag. Thirdly, by minimising thevertical velocity beneath and upward through the bag arrayre-entrainment of the duct cleaned off the filter bags is minimisedthereby lowering cleaning air/energy requirements and prolonging baglife. Fourthly, providing a more uniform distribution of dusty gasaround the bag bundle and into each individual bag, cleaning airrequirements will be minimised and bag life further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purposes of clarification, the present invention will now bedescribed by way of example only with reference to the accompanyingdrawings in which:

FIG. 1 is a perspective view of a fabric filter apparatus according tothe first embodiment of the present invention;

FIG. 2 is a sectional plan view of the apparatus of FIG. 1, and

FIG. 3 is a sectional elevational view along section III--III of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In the drawings the arrows indicate likely gas flow. Referring to FIG. 1the fabric filter apparatus 10 comprises a housing 11 having at itslower end an inwardly tapering hopper 12. The housing 11 is divided intoupper clean gas zone 20 and lower dusty gas zone 30. A porting plate 40is provided therebetween from which a circular array of filter bags 50depend. Please note that the relative sizes of the various componentsare not to scale.

The porting plate 40 has a series of radially spaced concentric ring ofports. Each of these ports communicates with a respective filter bag ofthe circular filter bag array 50. Above the porting plate is a gas pulsegeneration/distribution system 60 (see FIG. 3) substantially asdisclosed in U.S. Pat. No. 4,854,951 the contents of which areincorporated herein by reference.

The gas pulse generation/distribution system 60 includes a verticallyextending inlet tube 61 which is connected at its lower end to a pair ofradially extending gas manifolds 62 and 63. Each manifold 62 and 63extends across and above the porting plate 40 and carries a plurality ofdownwardly directed nozzles. The nozzles of manifold 62 are positionedso that they respectively rotate over one of the even numbered rings ofports while the nozzles of manifold 63 are positioned so that theyrespectively rotate over one of the odd numbered rings of ports. Clearlythe generation/distribution system 60 can be produced in alternativemanners as a matter of design preference. For example, the nozzles ofeach manifold 62 and 62 can be arranged as a plurality of equallyradially spaced pairs, each nozzle 25 of a respective pair aligning uponrotation with its respective ring of ports.

A dusty gas inlet 31 extends across one face of the housing 11 and openspreferably into hopper 12. As more clearly shown in FIG. 3, this inletcomprises an inlet hopper 32 and damper 33 disposed in the inlet hopperand adapted to control the volume of the gas flowing through the inlethopper 31 into housing 11. In the embodiment shown, the damper isprovided by a rotatable vane however any suitable air damper means maybe used.

The housing 11 includes at least one duct 13 the bottom of which is influid communication with inlet 31. The top of the duct 13 opens into thehousing 11 at a position intermediate the inlet 31 and the porting plate40. In the embodiment shown, two ducts 13 extend substantiallyvertically in adjacent corners of the housing, the bottoms of theseducts being in fluid with the communication with opposite lateral endsof inlet 31.

The inventive apparatus operates as follows. A vacuum is provided in theclean gas section 20 so that a first portion of the dusty gas is drawnthrough inlet 31 and into the housing 11 at a position adjacent or belowthe circular filter bag array 50.

Ducts 13 in housing 11 divert a second portion of the dusty gas enteringthe housing from the inlet 31 and deliver it to a corner of the housingat a level intermediate the porting plate 40 and inlet 32.

The ducts may be sized according to the amount of inlet flow to bediverted. Between 10% -90% of the total dusty gas entering the filtermay be diverted to a corner of the housing at a level intermediate theporting plate and the inlet.

This improves the flow patterns of the dusty gas around the circularfilter bag array by promoting a sidewards downwards gas flow to maximiseparticulate pre-separation. Further, since part of the inlet flow isdiverted this minimises the vertical velocity beneath and upwardsthrough the bag bundle thereby reducing re-entrainment of the dustcleaned off the filter bags. A more uniformed distribution of dusty gasaround the bag bundle is also provided.

The dusty gas in the housing is then drawn through the circular filterbag array 50 with the particulate matter in the dusty gas beingseparated by the filter bags. The clean air then passes through the openupper end of the filter bags into the clean air section 20 where it isremoved via outlet 21.

In a preferred embodiment, each inlet duct is provided with a smallbleed aperture 14 at its lower end so that any particulate matter thatmay drop out of he dusty gas stream in duct 13 may be discharged fromits lower end and directed into hopper 12.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

I claim:
 1. A fabric filter apparatus having a prismatic housingdefining a dusty gas section with an elongate horizontal inlet theretoand a clean gas section with an outlet therefrom, a porting platemounted in the housing separating the dusty gas section from the cleangas section and a substantially circular array of fabric filter bagsdepending therefrom, the inlet being adjacent the lowermost end of thefilter bags; said housing further including a generation/distributionmeans to generate pulses of back flushing gas and distribute themperiodically into the open upper ends of the fabric filter bags throughrespective ports in the porting plate, characterized in that respectivedusty gas flow ducts are located in each of two corners of the prismatichousing at opposed lateral ends of the inlet, said ducts being in fluidcommunication with the inlet so as to direct a portion of the dusty gasinflowing through the inlet upwardly of the housing to exit each duct ata level intermediate the inlet and the porting plate.
 2. A fabric filterapparatus as claimed in claim 1 wherein said housing is provided with aplurality of substantially planar sides, each duct extendingsubstantially vertically upwards in a corner of the housing from alateral end of the inlet.
 3. A fabric filter apparatus as claimed in anyone of claims 1 or 2 wherein said housing has four planar sides and isprovided with two substantially vertically oriented ducts, the inletextending along one side of the housing with each of the two ducts beingdisposed in adjacent corners of the housing.
 4. A fabric filterapparatus as claimed in any one of claims 1 or 2 wherein the lower endof the housing if formed by a downwardly tapering hopper, the inletopening into the hopper.
 5. A fabric filter apparatus as claimed in anyone of claims 1 or 2, wherein a damper is mounted in the inlet tocontrol the gas flow into the housing.
 6. A fabric filter apparatus asclaimed in any one of claims 1 or 2, wherein the duct is provided with ableed aperture at a lower portion thereof to allow escape of particulatematter falling out of the dusty gas in the duct.
 7. A method of feedinga dusty gas to a dusty gas section of a fabric filter within a prismatichousing, said filter further including a clean gas section, a portingplate mounted between the dusty gas section and clean gas section with acircular array of fabric filter bags depending from the porting plateand a generation/distribution means to generate pulses of back flushinggas and distribute them periodically into the open upper ends of thefabric filter bags through respective ports in the porting plate, saidmethod comprising feeding a first portion of the dusty gas directly intothe housing at a position below or adjacent the bottom of the filter bagarray and diverting a second portion of the dusty gas from a dusty gasinlet to the housing and delivering the diverted dusty gas to a levelintermediate the inlet and the porting plate via spaced apart ductsformed at opposed lateral ends of the dusty gas inlet to the housing. 8.A method of feeding a dusty gas to a dusty gas section of a fabricfilter as claimed in claim 7 wherein said inlet is provided by anelongated opening extending along a side of the housing, said dusty gasbeing diverted vertically upwards from a lateral end portion of saidinlet opening.
 9. A method of feeding a dusty gas to a dusty gas sectionof a fabric filter as claimed in claim 8 wherein said dusty gas isdiverted vertically upwards from both lateral end portions of theelongated inlet.
 10. A method of feeding a dusty gas to a dusty gassection of a fabric filter as claimed in claim 7 wherein said secondportion is between 10% and 90% of the total dusty gas flow entering thefilter.
 11. A method of feeding a dusty gas to a dusty gas section of afabric filter as claimed in claim 10 wherein said inlet is provided byan elongated opening extending along a side of the housing, said dustygas being diverted vertically upwards from a lateral end portion of saidinlet opening.
 12. A method of feeding a dusty gas to a dusty gassection of a fabric filter as claimed in claim 11 wherein said dusty gasis diverted vertically upwards from both lateral end portions of theelongated inlet.
 13. A method of feeding a dusty gas to a dusty gassection of a fabric filter as claimed in claim 7 wherein the housing isprovided with a plurality of substantially planar sides, the dusty gasbeing diverted vertically upwards from both lateral ends of theelongated inlet.